linux-kernel - perf tools: Options being passed to clang when building the BPF part of skels

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Date:   Tue, 22 Aug 2023 09:33:16 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...nel.org>, amadio@...stprotocols.net,
        Namhyung Kim <namhyung@...nel.org>,
        Guilherme Amadio <amadio@...too.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: perf tools: Options being passed to clang when building the BPF part
 of skels

Hi,

	On gentoo I'm noticing this:

clang-16clang-16: : clang-16error: : error: clang-16clang-16: clang-16clang-16clang-16: clang-16error: clang-16: : ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]: : : clang-16error: ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]error: error: : 
error: 
error: error: error: ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]error: ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]

ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]

ignoring '-fstack-protector-strong' option as it is not currently supported for target 'bpf' [-Werror,-Woption-ignored]

And while just doing:

diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index a5dd1ba..7726b57 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -1101,7 +1101,7 @@ else
 endif
 
 $(SKEL_TMP_OUT)/%.bpf.o: util/bpf_skel/%.bpf.c $(LIBBPF) $(SKEL_OUT)/vmlinux.h | $(SKEL_TMP_OUT)
-	$(QUIET_CLANG)$(CLANG) -g -O2 --target=bpf -Wall -Werror $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
+	$(QUIET_CLANG)$(CLANG) -g -O2 --target=bpf -Wall -Werror -Wno-option-ignored $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
 	  -c $(filter util/bpf_skel/%.bpf.c,$^) -o $@
 
 $(SKEL_OUT)/%.skel.h: $(SKEL_TMP_OUT)/%.bpf.o | $(BPFTOOL)


"Fixes" it, I'm curious as where is that we're setting up the options
that are being passed to clang at:

tools/perf/Makefile.perf

$(SKEL_TMP_OUT)/%.bpf.o: util/bpf_skel/%.bpf.c $(LIBBPF) $(SKEL_OUT)/vmlinux.h | $(SKEL_TMP_OUT)
        $(QUIET_CLANG)$(CLANG) -g -O2 --target=bpf -Wall -Werror $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
          -c $(filter util/bpf_skel/%.bpf.c,$^) -o $@

Perhaps it is plain just using CFLAGS? I.e. maybe the native build
CFLAGS is being passed to the BPF target clang calls?

Ideas?

- Arnaldo